High strip rate downstream chamber

ABSTRACT

A gas chamber contains upper and lower chamber bodies forming a cavity, a heating chuck for a wafer, a remote gas source, and an exhaust unit. Gas is injected into the cavity through channels in an injector. Each channel has sections that are bent with respect to each other at a sufficient angle to substantially eliminate entering light rays entering the channel from exiting the channel without reflection. The channels have funnel-shaped nozzles at end points proximate to the chuck. The injector also has thermal expansion relief slots and small gaps between the injector and mating surfaces of the chamber and gas source. The temperature of the injector is controlled by a cooling liquid in cooling channels and electrical heaters in receptacles of the injector. The upper chamber body is funnel-shaped and curves downward at an end of the upper chamber body proximate to the chuck.

RELATED APPLICATIONS

This patent application is a continuation patent application of, andclaims priority to, U.S. patent application Ser. No. 11/096,820, filedApr. 1, 2005.

BACKGROUND OF THE INVENTION Field of the Invention

The present application related to the field of wafer processing. Moreparticularly, the application relates to an etching chamber used inwafer processing.

Photoresist removal (stripping) is a frequently used process insemiconductor integrated circuit (IC) fabrication. Photoresist is usedto define particular patterns on wafers. It is used during lithography,ion implantation and plasma etching (where material other than thephotoresist is removed), for example. After these processes, thephotoresist is removed from the wafers before continuing to the nextprocess.

Since photoresist stripping is used frequently in semiconductormanufacturing foundries, strippers are designed to have very shortprocess time, i.e. high throughput, to reduce the overall wafermanufacturing cost. While different ways exist to increase a stripper'sthroughput, they fall into two categories: overhead reduction and striprate improvement. Overhead includes wafer handling time, pump down timeof the chamber into which the wafer is loaded, stabilization of pressureinside the chamber, wafer heating, and backfill of the chamber with adesired gas, all of which prepare a wafer for the particular process.The strip rate is a measure of how fast the photoresist is removed andcleaned from the wafer surface. The strip rate also determines how longa wafer is exposed to plasma. A wafer's exposure time to plasma in astrip chamber is generally minimized to reduce the possibility ofelectrical damage to various circuits on the wafer. The strip rate canbe increased by using a higher plasma source power, higher wafertemperature, higher process gas flow or changing the gas chemistry.

Most strippers have an entrance hole through which a gas is injectedinto a chamber containing a wafer to be processed. The typical verticaldistance between the entrance hole and the wafer is a few inches. Thisdistance is minimized so that the chamber is compact and economical tomanufacture. To obtain a uniform strip pattern, a uniform vertical flowfor the gas at the wafer surface is maintained. At typical flow ratesthat are used, however, the gas will not fan out in a few inches. Thus,to achieve a uniform flow in such short distance, a gas dispersionsystem is used to disperse the gas stream to the wafer.

As shown in FIG. 1, a known stripper 100 contains a downstream chamber102 in which the wafer 130 is exposed to the gas. The wafer 130 is heldby a chuck 120. The gas 106 enters the downstream chamber 102 through anentrance hole 104. As the gas 106 enters the chamber, a gas dispersingsystem such as a baffle 110 disperses the gas 106 to distribute the gas106 evenly onto the wafer 120. The strip uniformity and the strip rateare highly dependent upon this gas dispersing system. As shown in FIGS.1 and 2, the baffle 110, 200 contains a large number of holes 112, 202of different sizes. More specifically, the sizes of the holes increasewith increasing distance from the center of the baffle because thecenter of the baffle receives more gas flow than does the edge. The gas106, after acting on the wafer 120, exits from an exit port 108.

Other strippers 300 contain a downstream chamber 302 in which the wafer330 is exposed to the gas as shown in FIG. 3. The wafer 330 is held by achuck 320. The gas 306 enters the downstream chamber 302 through anentrance hole 304. As the gas 306 enters the chamber, a multiple bafflesystem baffle disperses the gas 306 to distribute the gas 306 evenlyonto the wafer 320. The first baffle 310 contains holes 312, 314 of twodifferent sizes similar to that described above. The second baffle 316contains holes of only one size, which are offset from the holes in thefirst baffle 310 so gas molecules that pass through the holes on thefirst baffle 310 have to make two 90° turns before leaving the holes atthe second baffle 316. The gas 306, after acting on the wafer 320, exitsfrom an exit port 308.

Although not shown, in another design to disperse gas, a showerhead isused. A showerhead is similar to a baffle, however, the number and sizeof holes are such that they create a back pressure. Back pressures ofabout 10 Torr or greater are produced by such a design. The creation ofthese back pressures effectively slows down the gas flow above theshowerhead and reduces the effect of flow dynamics.

However, it is complicated to optimize the hole sizes and pattern forthe single baffle design. Baffles used in single baffle designs are alsoexpensive to manufacture due to the various sizes and the large numberof holes. Similarly, while multiple baffle designs may simplify the holepattern, the use of multiple baffles increases the size and weight ofthe chamber, as well as increasing the cost of material, if notfabrication. In showerhead designs, the higher up stream pressure notonly lowers the ionization efficiency of the gas source but alsoincreases the radical recombination, and consequently lowers the striprate.

Furthermore, the large surface area created by the baffles or showerheadand the internal shape of the upper chamber permit rapid neutralizationof the radicals in the gas, which actually produce the stripping of thephotoresist. Without a baffle, the stripping rate is two to three timesas much as that with a baffle. This means that the baffle neutralizesmore than half of the radicals generated by the gas source.

SUMMARY OF THE INVENTION

A gas chamber is provided with a chamber design and gas dispersingcomponent designed to improve gas flow and increase the strip ratewithout using expensive single or multiple baffles. By way ofintroduction only, in one embodiment, an apparatus contains upper andlower chamber bodies forming a cavity, a gas source providing gas forthe cavity, an exhaust unit through which the gas in the cavity isremoved, a chuck disposed in the cavity and an injector containingchannels extending therethrough. Each channel is bent enough tosubstantially block light rays entering the channel from directlyexiting the channel, i.e. from exiting the channel without undergoing atleast one reflection within the channel.

In another embodiment, the apparatus contains a single fixture betweenthe gas source and the cavity through which the gas passes to enter thecavity. The fixture has channels with portions that bend at asubstantially perpendicular angle from each other.

In another embodiment, the apparatus contains an injection means forintroducing the gas from the gas source into the cavity through channelswhile blocking radiation from the gas source from passing through thechannels. In various further embodiments, ends of the channels maycomprise ejection means for angling gas ejected from the channels intothe chamber at angles different from angles of the channels; the upperchamber body may comprise guiding means for guiding the gas in thecavity ejected by the injection means; and/or the injection means maycomprise means for absorbing thermal expansion of the injection means,means for eliminating rubbing of mating surfaces of the injection meansand at least one of the upper chamber body and gas source, and/or meansfor adjusting a temperature of the injection means.

In another embodiment, a method includes injecting a gas into a cavity,towards a wafer, through channels in an injector that bend enough toprevent light from passing straight through the channels, the cavityformed by upper and lower chamber bodies, shaping the flow of the gasusing at least angles of the channels through which the gas flows,angles of ends of the channels from which the gas is ejected, and anglesof internal surfaces of the upper and lower chamber bodies, and removingthe gas that has impinged on the wafer through an exhaust vent.

In a further embodiment, at least one of the channels has a firstinclination angle in an upper section of the injector substantiallyperpendicular to a second inclination angle of a lower section of theinjector. At least one of the first and second inclination angles may beoblique from a central axis of the injector. The first inclination anglemay range from about 0° to 60° from the central axis of the injectorwhile the second inclination angle ranges from about 10° to 60° from thecentral axis of the injector.

In another embodiment, a nozzle at an end of at least one of thechannels has a diameter greater than a diameter of the remainder of thechannel. The diameter of the nozzle may increase with decreasingdistance to the end of the channel and be funnel-shaped. An angle at theend of the nozzle adjacent to an internal surface of the upper chamberbody may match an angle of the internal surface. The internal surfacemay be funnel shaped and the internal surface of the upper chamber bodyadjacent to an internal surface of the lower chamber body curvedownward. The internal surface of the upper chamber body may be funnelshaped and curve downward toward the chuck.

In another embodiment, the injector has a tapered lower portion, whichmay have first and second regions that taper at different rates. Theinternal surface of the upper chamber body may match an angle of taperof at least one of the first and second regions.

In another embodiment, the injector is disposed between the gas sourceand the cavity. The injector may be attached to and contact the gassource. O-rings may be disposed between the injector and the gas sourceand between the injector and the upper chamber body and the injectorcontain a slot that is substantially parallel to a central axis of theinjector inside at least one of the O-rings. Alternatively, the injectormay contain a gap inside the O-ring between at least one of a surface ofthe injector and a surface of the gas source; and a surface of theinjector and a surface of the upper chamber body.

In another embodiment, the injector contains a temperature adjustmentsystem that permits manual or automatic adjustment of a temperature ofthe injector. The temperature adjustment system may comprise a coolingchannel with a cooling liquid in the injector, and a temperature sensorthat senses the temperature of the injector and an electrical heaterthat alters the temperature of the injector.

The following figures and detailed description of the preferredembodiments will more clearly demonstrate these and other aspects of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a known single-baffle stripper chamber.

FIG. 2 illustrates the baffle of FIG. 1.

FIG. 3 illustrates a known multi-baffle stripper chamber.

FIG. 4 illustrates a gas chamber according to one aspect.

FIG. 5 illustrates a perspective view of a dispersing componentaccording to one aspect.

FIG. 6 illustrates a cross-sectional view of a dispersing componentaccording to a second aspect.

FIG. 7 illustrates a cross-sectional view of a dispersing componentaccording to a third aspect.

FIG. 8 illustrates a cross-sectional view of a dispersing componentaccording to a fourth aspect.

FIG. 9 illustrates a cross-sectional view of a dispersing componentaccording to a fifth aspect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A gas chamber is described for improving flow of a gas and increasing astrip rate of photoresist on a wafer disposed within the chamber. Thegas chamber has a tailored upper chamber body and a gas injector thatdisperses the gas around the chamber while having a very small surfacearea to which the gas is exposed. In addition, the gas injector issmaller than known baffles or showerheads, as well as being moreeconomical to manufacture due to its smaller size and relatively simpleand short machining process. The term gas, as used herein, includes agas containing radicals, i.e. a plasma.

In a stripping process using a gas, typically the gas has a high flowrate and high pressure. As one example, the flow rate of the gas can be5 standard liters per minute (slm) at 1 Torr. For a gas, the mean freepath at this pressure can be obtained with the following equation:

$L = \frac{kT}{\sqrt{2\pi \; {Pd}^{2}}}$

where L is the mean free path of the gas, k is the Boltzmann constant, Tis the absolute temperature of gas, P is pressure and d is the diameterof the gas molecule. As one example, the mean free path of an oxygenmolecule is around 0.06 mm at room temperature. When a gas is ignited,however, the gas temperature rises dramatically. If the gas temperaturerises to 1000° K., the mean free path of oxygen increases to around 0.2mm. These values are much smaller than any geometric feature of awafer-processing chamber. The gas flow may be treated as, therefore, aviscous flow in which Newtonian gas dynamics dominates.

A high gas stream velocity is the direct result of high gas-flowprocesses. A typical recipe for stripping photoresist from the surfaceof a semiconductor wafer calls for a flow rate of 5 slm O₂/N₂ at 1 Torr.Under these flow and pressure conditions, the gas velocity leaving thegas source with an exit diameter of 2.5 cm, for example, is around 177m/sec. To obtain a uniform strip pattern, a uniform vertical gas flow atthe wafer surface is used. At 177 m/sec, the gas will not typicallydisperse uniformly across the surface of the wafer unless a dispersalunit is present in the gas flow.

As shown in FIG. 4, the gas chamber 400 contains upper and lower chamberbodies 402 and 404, a remote gas source 440, and an exhaust unit 450.The upper and lower chamber bodies 402 and 404 form a cavity 416 inwhich a vacuum is generated. An O-ring 406 disposed between the upperand lower chamber bodies 402 and 404 permits the vacuum to bemaintained. The gas source 440 is microwave or RF-powered and excites aprocess gas entering the source and creates a plasma. Typical gasesinclude oxygen, nitrogen, chlorine, argon, xenon depending on thedesired process. The gas source 440 typically contains a gas transporttube 442 that contains sapphire.

The gas source 440 is attached to the upper chamber body 402 of the gaschamber 400 using screws or bolts. The gas source 440 communicates withthe upper chamber body 402 through an injection port 414 such that thegas is transported downstream to the upper chamber body 402 throughchannels 412 in an injector 410. In one embodiment, the injection port414 has a diameter of about 2.5 cm, which is the same size as a typicalgas transport tube 442 of the gas source 440. The gas source 440 ispreferably cooled, by water for example.

Once the gas has been dispersed by the injector 410, it is confined bythe walls of the cavity 416 in the upper chamber body 402 and impingesevenly on a wafer 420 disposed on a temperature controlled chuck 430.The injector 410, wafer 420 and chuck 430 are disposed in the cavity 416formed by the upper and lower chamber bodies 402 and 404. In oneembodiment, the cavity 416 has a diameter of about 33 cm to 41 cm and aheight of about 10 cm to 30 cm. Although the wafer 420 may have anydiameter, typically 6 inch, 8 inch or 12 inch wafers are used insemiconductor fabrication.

The gas, in one embodiment, ashes a photoresist layer remaining from anearlier process. The earlier process may be any semiconductorfabrication process, for example, ion implantation, etching, or metaldeposition. The gas is then drawn from the lower chamber body 404 via anexit port 408 and through a series of vacuum components by a vacuum pump458. These vacuum components include, for example, a vacuum line 452, anisolation valve 454, and a throttle valve 456.

In FIG. 4, the injector 410 is located right below the gas source 440and above the upper chamber body 402. There are multiple flow channels412 inside the injector 410. The flow channels 412 are angled away fromthe center line of the upper chamber body 402. The angled flow channelsdivide and direct the gas stream from the source evenly toward the wafer420. The diameter and number of the flow channels are selected so thatthey provide uniform gas distribution over the wafer but do not create alarge amount of back pressure in the gas source 440. A high backpressure in the source can result in poor gas ionization and highradical recombination.

For a chamber pressure of 1 Torr and a flow rate of 5 slm, the injector410 creates a back pressure of about 4 Torr in the gas source 440, wellbelow the 10 Torr back-pressure which severely decreases the number ofradicals produced in the gas source 440. In this example, the injector410 has a gas-exposed surface area of about 46 cm², which includes thetop surface, the walls of the flow channels and the bottom surface ofthe injector 410. As a comparison, the single baffle structure of FIG. 1has a surface area of over 2000 cm².

While radicals can still recombine inside the flow channels 412 ofinjector 410 due to collision of the molecules with the channel walls,the recombination is minimal due to the small channel wall surface andthe high gas velocity inside the flow channels 412. The diameters of theflow channels 412, although small, are still much larger than the meanfree path of the gases flowing therethough at the pressure andtemperature used. The average velocity of the gas flowing through theflow channels 412 and under the flow conditions stated previously isaround 260 m/sec. At this flow rate, it only takes a molecule about 12μs to travel through the flow channels 412. Therefore, only a smallamount of radicals are neutralized when passing through the flowchannels 412.

In one example, as shown in the perspective view of FIG. 5, the injector500 contains six flow channels 502. Each flow channel has a diameter ofabout 0.4 cm and is about 2.7 cm long. Although FIG. 5 shows a sixchannel injector, an injector with additional or fewer channels may beused as desired. FIG. 6, for example, shows a four channel injector 600.As can be seen by the cut-away view, the channels of the injectorcontain one or more bends. Each channel is bent at a sufficient angle tominimize or eliminate ultraviolet (UV) rays and charged moleculesgenerated in the gas source where the gas is ionized from substantiallypassing directly from the entrance of the channel to the exit of thechannel. In other words, the UV rays do not substantially pass from theentrance to the exit without being reflected. If not properly blocked,the UV rays and charged molecules can travel to the wafer and damage thecircuit.

As shown in FIG. 6, the injector 600 has an upper portion 610 and alower portion 612. The upper portion 610 is substantially cylindricaland is used to couple the injector 600 to the remote gas source and theupper chamber body, discussed in more detail below. The lower portion612 has first and second regions 614 and 616 that taper at differentrates with increasing distance from the remote gas source. The lowerportion 612 has a smaller diameter than the diameter of the upperportion 610. The first and second regions 614 and 616 may have othershapes, e.g., spherical or cylindrical. Similarly, although the firstand second regions 614 and 616 are shown as tapering at different rates,the first and second regions 614 and 616 may have the same taper (e.g.,be substantially a single conical or spherical structure) or have notaper (e.g., be substantially cylindrical with one or more cylinders ofone or more diameters).

In addition, each channel 602 has an upper section 604 and a lowersection 606. The lower section 606 contains a nozzle 608 from which thegas is ejected. The diameter of the channel 602, except the nozzle 608,remains substantially constant. The nozzle 608 has a diameter thatincreases with decreasing distance to the end of the channel 602. In theembodiment shown, the nozzle 608 is substantially funnel-shaped.

The upper section 604 of one channel has an inclination angle A from thecentral axis of the injector 600 that is substantially perpendicular tothe angle B of the lower section of the channel. The angle of the lowersection 606 determines the angle of the gas exiting the flow channel 602and is used to adjust the flow pattern at the wafer. Gas flow is morefocused toward the center with smaller angles, and is more spread-outwith larger angles. Different flow and pressure conditions and gas typesmay use injectors with different angles to be optimized for best overallperformance. For example, angle A ranges from about 0° to 60° from thecentral axis of the injector 600 while angle B ranges from about 10° to60° from the central axis of the injector 600.

By using perpendicular planes of angles for the upper and lower section604 and 606, a direct line of sight through the channel 602 can beavoided. Thus, UV rays can be blocked while the B angle can be varied tooptimize the design of the injector for strip uniformity. Moreover, toreduce ions reaching the wafer, the injector forces the ionized gasstream to turn sharply. Sharp turns facilitate wall collision andtherefore help to neutralize ions. This permits a controlled reductionin the number of ions leaving the injector. Note that although onlychannels with a single bend (i.e. only two sections) are shown, thechannels may have multiple sharp bends (i.e. more than two sections).Alternatively, the channels may be curved to eliminate line-of-sightfrom the entrance to the exit of the channel and force the gas moleculesto collide with the surface along the curve.

In other examples, the diameter of the injector may range from about 5cm to 13 cm, while the thickness ranges from about 1 cm to 13 cm. From 3to 24 flow channels are present in the injector. These flow channelshave a diameter that may range from about 0.3 cm to 1 cm and extend inlength from about 1 cm to 5 cm.

Strip uniformity is affected by different features in the chamber. Theangle of the lower channel of the injector controls the direction of thegas streams coming out of the nozzles, and thus alters the stripuniformity from the center to the edge of the wafer. The flaring exit ofthe nozzle helps fan out the gas stream coming out of the nozzle, andthus improves the circumferential uniformity.

In addition, the funnel-shaped upper chamber body, shown in FIG. 4,affects the gas flow pattern after the gas exits from the injector. Theinner surface of the upper chamber body is continuous so that the gasflowing out of the injector is confined in the upper chamber body. Thefunnel shape lessens recirculation of the gas after the gas has left theinjector. The funnel surface curves downward when reaching the lowerchamber body (or the edge of the wafer), which further confines andguides the gas to control the strip rate at the wafer edge.

The funnel shape of the top of the upper chamber body reduces the volumeof the space formed by the upper and lower chamber bodies compared withthe volume used by the cylindrical upper chamber body shown in FIGS. 1and 3. This reduces the amount of time it takes to pump down the chamberfrom atmospheric pressure to the pressure used during the process aswell as reducing the amount of time it takes to vent to the atmosphere.Some strip chambers use pumping and venting for every wafer processed,resulting in a large decrease in throughput, i.e. a large increase intime to process, for a batch of wafers. Other strip chambers, which aredesigned to cluster around a central wafer-transferring vacuum chamber,use partial venting to a pressure higher than the process pressure toimprove the heat transfer between the chuck and the wafer. The chamberis then pumped down to the process pressure after the wafer heating iscomplete.

Control of the injector's temperature helps to achieve consistentprocess results. For example, the surface recombination efficiency ofthe gas radicals recombining on the surface of the injector varies withthe temperature of the surface. Depending on the gas chemistry, therecombination rate can be proportional to the temperature or can beinversely proportional to the temperature. However, it can be difficultto regulate the typical baffle's temperature due to the size of thetypical baffle shown in FIGS. 1 and 3. When the temperature of thebaffle varies, the process results may differ from wafer to wafer. It isalso difficult to keep a baffle's temperature uniform. For the chambersshown in FIGS. 1 and 3, the temperature of the baffle is higher at thecenter of the baffle since this area is directly under the plasma sourceand receives more heat load than other areas of the baffle. Anon-uniform temperature profile causes the baffle surface to havenon-uniform radical recombination efficiency, which further complicatesthe process.

However, as the injector is significantly smaller than the typicalbaffle, it is easier to control the injector's temperature. FIG. 7illustrates a close up cross-sectional view of one embodiment of the gaschamber 700. The gas chamber 700 contains an upper chamber body 702, aninjector 710 and a gas source 750. The gas source 750 is coupled to theupper chamber body 702 by screws 730. Similarly, the injector 710 iscoupled to the gas source 750 by screws 740. The gas source 750generates plasma 752, which is supplied through the channels 712 in theinjector 710 to the upper chamber body 702. The gas source 750 containsa recess in which an upper vacuum O-ring 720 is disposed, while theupper chamber body 702 contains a recess in which a lower vacuum O-ring722 is disposed. The injector 710 also includes slots 716 and gaps 718,as discussed below.

As shown in FIG. 7, to keep the temperature under control, the injector710 is designed to have a large thermal contact area, which is atatmospheric pressure. The thermal contact area is the area of theinjector 710 outside the vacuum O-rings 720, 722. The screws 730 and 740provide tight contact between the injector 710 and the gas source750/upper chamber body 702 to produce a good heat transfer path betweenthe thermal contact area and the gas source 750. The thermal energyreceived from the plasma 752 is transferred to the gas source 750 or tothe upper chamber body 702 through the thermal contact area. Thetransfer of this energy is efficient enough to maintain the injector ator below a desired temperature.

As shown in FIG. 8, the injector 800 can also be formed with one or morecooling channels 820 that contain a cooling liquid 822, which permits alarger amount of heat to be removed. To maintain the injector 800 at aconstant temperature, the cooling fluid 820 can be circulated through atemperature control unit (not shown). The injector's temperature canthen be controlled by setting the temperature of the cooling liquid 822at the temperature control unit. The cooling liquid in each coolingchannel can be the same or different.

If active temperature control is desired, a combination of heating andcooling may be used. Electrical heaters 960, as shown in FIG. 9, can beinserted into the injector 900 separately from the cooling channels 920.The electrical heaters may be, for instance, resistors. A temperaturecontroller 950 can be used to control the current to the electricalheaters 960 to adjust the temperature of the injector 910. The heaters960 may be controlled individually or in one or more groups.Additionally, one or more temperature sensors 970 may be inserted intothe injector 900. The temperature sensor 970 may be, for example, athermocouple or Resistance Temperature Detector (RTD). Alternatively,thermoelectric elements can be used to control the temperature of theinjector, replacing the heaters and cooling channels.

Besides process variation, temperature changes of the various componentsin the gas chamber may cause other problems. For example, even withrelatively good heat transfer, the injector's temperature is stillhigher than that of the mating parts (e.g. the gas source and the upperchamber body). Thermal expansion mismatch between the injector and themating parts in the injector area produces mechanical stress. Thismechanical stress can deform or damage the injector or the mating parts.To alleviate this, one or more slots 716 are formed in the injector 710.The slots 716 are circular vertical slots on each side of the injector710, which act as thermal expansion relief slots.

In addition, thermal mismatch may cause particle contamination. As theinjector heats up and cools down, it expands and contracts relative tothe mating parts. As a result, rubbing occurs between mating surfaces ofthe injector and the mating parts. Rubbing creates particles, which ifintroduced are detrimental to wafers in the chamber. To avoid rubbing ofthe mating surfaces, a small gap 718 of 0.13 mm or less is introducedbetween the mating surfaces inside the vacuum O-rings 720 and 722.Although gaps can be provided in areas outside the O-rings 720 and 722,they are not shown in FIG. 7 as the O-rings 720 and 722 effectivelyexclude particles outside the O-rings 720 and 722 from entering thechamber 700.

The injector and the upper and lower chamber bodies as well as theinjector can be manufactured using all plasma-resistant material. Theplasma-resistant material can be formed from metallic or non-metallicmaterial. If one or more metals are used to form the injector, theinjector can include, for example, aluminum and aluminum alloys,stainless steel and high nickel alloys, quartz, aluminum oxide ceramic,aluminum nitride ceramic, and/or yttrium oxide ceramic.

Parts fabricated using metals can be protected against corrosion withplasma resistant coatings. In one example, aluminum may be used as itsnatural surface oxide provides an excellent corrosion barrier. However,when using fluorine based chemistry and under certain processconditions, the aluminum native oxide does not provide sufficientprotection to avoid formation of aluminum fluoride, which causescontamination on wafers. To prevent metallic fluorides from forming onmetal parts, coatings that have superior resistance to fluorinechemistry can be applied to the surface of metal parts. Coatings such asanodization over aluminum and its alloys and plasma sprayed aluminumoxide, nickel plating, quartz, yttrium oxide and/or other ceramicmaterials may be used for protection from various chemistries.

Turning back to FIG. 4, the wafer 420 lies on a wafer heating chuck 430in the chamber. Before strip process can be conduced, wafers are heatedto a temperature high enough to accelerate the chemical reaction. Waferheating is non-trivial as the strip uniformity is directly related tothe temperature uniformity at the wafer. The wafer is heated as quicklyas possible to reduce the time the wafer is in the chamber that isnon-productive. Although electrostatic chucks may be used in stripperapplications, they are expensive and may not be reliable. However, anelectrostatic chuck has an electrically-induced clamping force thatpulls the wafer closer to the chuck for good heat transfer, which anon-electrostatic chuck may not have. One way to mitigate such a problemis to control the flatness of the chuck to within a particular amount.In one example, to provide a fast heat transfer and uniform wafertemperature when using a non-electrostatic chuck, the non-electrostaticheater chuck has a global flatness of better than about 27 μm.

In addition, pumping of the chamber affects the strip rate of thephotoresist on the wafer. Strip processes are usually high-flow (e.g.,several slm) and high-pressure (e.g., 750 mTorr or higher). Accordingly,strip processes are not entirely in either a viscous flow regime or amolecular flow regime. To provide uniform pumping, a single pump port408 is located at the center of the lower chamber body 404.

Other systems can be incorporated in the chamber to improve the processresults. An optical spectrum end-point detector, for example, is onesuch system. Either a narrow band or a broad band optical wavelengthdetector is attached to a view port at the side of the chamber lookingdirectly at the bulk plasma above the wafer plane. The chemical reactionat the wafer surface between the photoresist and the plasma emits aparticular signature spectrum. Once the photoresist is depleted, thisspectrum changes immediately. This optical signal change determines theend of the strip process. End point detection has become sophisticatedenough to determine the transition of multi-layer strip process such ashigh dose implanted resist removal. This type of resist has a hard crustdue to the implant process. Chemistry designed to break through thecrust is different from that designed to strip the rest of the resistunder the crust. With proper setup, an optical detector is able todetermine this transition as the optical spectrum changes when the crusthas etched through. This change of signal allows the software to changethe chemistry in the plasma and switch to a different recipe for thebulk resist removal. However, systems such as the optical spectrumend-point detector described above add cost, weight and size.

A gas chamber has been described that contains a single injector havingchannels through which a gas passes into a vacuum chamber. The channelshave portions that are substantially perpendicular to each other. Theportions are disposed at angles of up to about 60° from a central axisof the injector. The channels have funnel-shaped end portions. Thechamber has a tapered upper portion that is matched to the angle of thefunnel-shaped end portions of the injector and disperses the gas ejectedfrom the injector. The injector is small and relatively simple tomanufacture.

While specific embodiments have been described, the descriptions hereinare illustrative only and not to be construed as limiting the invention.Various modifications, such as differences in materials and/ordimensions, and applications may occur to those skilled in the artwithout departing from the true spirit and scope of the invention asdefined in the appended claims.

1. A method of processing a wafer, the method comprising: injecting agas into a cavity, through channels in an injector that is bent enoughto substantially prevent light from passing through the channels withoutreflection; shaping the flow of the gas using at least angles of thechannels through which the gas flows; and removing the gas that hasimpinged on the wafer through an exhaust vent.
 2. The method of claim 1,further comprising providing each of the channels with substantiallyperpendicular bends, each bend being at most about 60° degree from acentral axis of the injector.
 3. The method of claim 1, furthercomprising providing a funnel-shaped nozzle at the end of each of thechannels.
 4. The method of claim 3, further comprising providing anupper chamber body with a funnel-shaped internal surface.
 5. The methodof claim 1, further comprising providing the injector with slots toabsorb thermal expansion of the injector.
 6. The method of claim 1,further comprising providing gaps between mating surfaces of theinjector and at least one of an upper chamber body and a gas source thatsupplies the gas.
 7. The method of claim 1, further comprisingcontrolling a temperature of the injector.
 8. An apparatus fordelivering gas to a substrate, the apparatus comprising: a cavity; a gassource in fluid communication with the cavity; an exhaust unit adaptedto remove gas from the cavity; and an injector disposed in the cavityand comprising a plurality of channels extending therethrough, eachchannel is in communication with the cavity and the gas source, whereineach channel has an upper section and a lower section, where theintersection between the upper section and the lower section is at anangle sufficient to prevent any light ray which enters the upper sectionof the channel from exiting the lower section of the channel withoutreflecting from a surface in the channel, wherein at least one channelin the injector has a first inclination angle in the upper section ofthe injector and a second inclination angle in the lower section of theinjector where the first inclination angle ranges from about 0° to 60°from a central axis of the injector while the second inclination angleranges from about 10° to 60° from the central axis of the injector. 9.The apparatus of claim 8, wherein a nozzle at an end of at least one ofthe channels is substantially funnel shaped.
 10. The apparatus of claim8, wherein the injector has a lower portion that is tapered.
 11. Theapparatus of claim 10, wherein the tapered lower portion has first andsecond regions that taper at different rates.
 12. The apparatus of claim8, wherein the injector contacts the gas source.
 13. The apparatus ofclaim 12, further comprising O-rings between the injector and the gassource, wherein the injector contains a slot inside at least one of theO-rings, the slot substantially parallel to the central axis of theinjector.
 14. The apparatus of claim 8, wherein the injector furthercomprises a temperature adjustment system that permits manual orautomatic adjustment of a temperature of the injector.
 15. The apparatusof claim 14, wherein the temperature adjustment system comprises acooling channel within the injector.
 16. The apparatus of claim 15,wherein the temperature adjustment system further comprises atemperature sensor that senses the temperature of the injector and anelectrical heater that alters the temperature of the injector.
 17. Anapparatus comprising: an upper and lower chamber bodies forming acavity; a gas source in fluid communication with the cavity; an exhaustunit adapted to remove gas from the cavity; and a fixture between thegas source and the cavity, the fixture having channels, where eachchannel extends from a upper portion the fixture adjacent to the gassource to a bottom portion of the fixture adjacent to the cavity andincludes at least two connecting segments disposed within the fixturethat are bent at substantially right angles with respect to each other,through which gas passes from the first end through the second end toenter the cavity.
 18. The apparatus of claim 17, wherein an end of oneof the at least two connecting segments of at least one channel isfunnel shaped.
 19. The apparatus of claim 18, wherein a portion of thefunnel shaped end is coplanar with an internal surface of the upperchamber body.
 20. The apparatus of claim 19, wherein the internalsurface of the upper chamber body is funnel shaped.